DE2728316A1 - LARGE PROCESS FOR THE PRODUCTION OF SODIUM DITHIONITE - Google Patents

Description

Process in batches for the production of sodium dithionite "

June 24, 1976 - V.St.A. - registration no. 699

Ik. June 1977 - V.St.A. (Registration no. Not yet known)

The present invention relates to an improved process for the preparation of anhydrous alkali metal hyposulfites, the are also known under the name Dithionite. In particular, the invention relates to an improved method of manufacture of sodium dithionite by reacting sodium formate with sulfur dioxide. The reactants are in an aqueous methanolic solution reacted with each other, in which both the alkali metal formate in question and sulfur dioxide are dissolved are.

Alkali metal dithionites are widely used as technical

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Bleaching agents used, for example for bleaching wood pulp. Zinc dithionite used to be used for this purpose used, which has been replaced a long time ago by sodium dithionite, because the zinc dust required for the production of zinc dithionite is a scarce commodity and therefore is only available at increased costs. In addition, there are also concerns about the environmental protection Use of zirconite because the corresponding zinc-containing Wastewater can only be processed with difficulty.

Sodium dithionite can be used both electrolytically and under Making use of borohydride. However, processes are particularly economical in which the formation is used to to reduce the value of the sulfur atom. In this way a solid end product of high quality can be produced in a particularly economical manner.

This process development began in 1933 with US Pat. No. 2,010,615, in which a process for the production of anhydrous alkali metal dithionites is described, according to which gaseous sulfur dioxide is introduced into an aqueous methanol solution containing sodium formate and sodium carbonate and at a temperature below 30 ⁰ G is held. The temperature of the methanolic SO solution is then increased to such an extent that the formation of sodium dithionite begins. In one embodiment, the amount of sodium carbonate used is 19.0 % of the sodium formate used. There is therefore a considerable excess in this known method

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of sodium formate is required to buffer the acidity of the solution, but at the same time the difficulty arises that the crystals formed are extremely fine and therefore show only poor stability.

About 30 years later, a number of improvements have been proposed, which are essentially based on the use of sodium hydroxide as a source of alkali. In this regard, reference is made to the following references: US Pat. Nos. 3,411,875, 3,576,598, 3,714,3 ¹ K), 3,718,732, 3,872,221, 3,887,695 and 3,897 SM; JA-PSen IOO3 / 68 and 2405/71 as well as BE-PS 698 247.

In these improved processes, the SO -containing methanol solution and an alkaline compound become an aqueous one Solution of an alkali metal formate added and the aqueous methanol solution obtained thereby is at a reaction temperature kept above the dewatering point of hydrated alkali metal dithionite to prevent the formation of crystals, which contain water of crystallization included. The rate at which the reactants are added must correspond to the rate at which the dithionite is produced. If the additional rate is too high, the dithionite ion just formed decomposes and the yield decreases accordingly.

Other suggested improvements are that sulfur dioxide is first in a water-miscible alcohol Feed solution is absorbed that also sodium hydroxide and sodium formate outside the reactor in very hot

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Water to be dissolved as the second feed solution and that both solutions are fed into the reactor, which is kept at a temperature in the range of 60 to 90 ° C and one Contains a small amount of the alcohol under superatmospheric pressure.

According to US Pat. No. 3,887,695, higher concentrations of Reactants used in the reactor also allow a higher production of the desired dithionite per unit volume of the reactor and depending To achieve a unit of volume of the alcohol used. For this purpose, methyl formate, which is a by-product in a previous reaction cycle can arise, dissolved in that part of the methyl alcohol, which is presented in the reactor and to which the feed solutions are then added.

Although the more recent improved processes use sodium hydroxide essentially as the sole source of supplying the required alkali and hardly any sodium carbonate Is mentioned; it should be pointed out that the JA-PS 7003/68 teaches, first of all, sulfur dioxide To dissolve concentration in methanol and then gradually add an aqueous alkaline solution which contains both sodium formate and sodium carbonate, namely the latter Compound in an amount of 33 percent by weight based on the sodium formate. The yield of sodium dithionite in this Process is 56 Ϊ, based on the sulfur dioxide used and 54 Z, based on the total sodium used.

Tables I and II below are the most important

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Data and results for the 15 working examples compiled, which are contained in the four major US patents as prior art. Data relating to the properties of the dust (Dust number) of these products are not accessible,

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• - ■ sas

Table I.

U.S. Patent 3,411,875

Example 12 3 4

NaOH, parts by weight 23 21 20 30 Na ₂ CO ₃ ,

H ₂ O, "200 240 136 100

HCOONa, ^H 80 90 70 75

CH ₃ OH, "470 500 386 424 HCOOCH ₃ ,"

SO ₂ , "80 87 72 100

Na ₂ S ₂ O ₄ , gross / 100% base 84 / 76.0 90 / 78.3 72 / 64.1 104 / 94.2

Purity,% 90.5 91.2 89.0 90.6

Temperature range, ° C 60 - 70 70 70 70

Total reaction time, hrs 4.8 5.3 5.0 5.3

Spreading rate, kg / h / l - - - 0.0228

Total Na equivalents 1.751 1.848 1.529 1.853

Total formate equivalents 1.176 1.323 liters, O29 1.103

Total SO ₂ equivalents 1.249 1.358 1.124 1.561

Total CH ₃ OH equivalents 14.669 15.605 12.047 13.233

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example

NaOH, _{parts by weight Na 2} CO ₃ , "H ₂ O, HCOONa," CH ₃ OH, "HCOOCH ,, ^S0 2 '

Na ₂ S ₃ O ₄ , gross amount, parts by weight Na-S ₀ O ₇₁ , 100% basis purity,% temperature range, C total reaction time, hourly yield, kg / h / l total Na equivalents total formate equivalents total S0 ₂ equivalents total CH ₃ Oh equivalents

T a
I. 2 5 bark
[JS-PS 3 714 , 0 , 5 II
340 , 2 , 0 4th U.S. PS 3 887 695 - 7 - KJ 1 8th 0257 2 - 3 , 0351 23.2 1 2 κ;
OO
co 23, 168 30 ₍ , 6 , 891 23, , 168 133.7 550 650 108 3 588 98 , 141 100 , 588 90 880 880 108 614
184 77 , 561
, 265 108 , 614
, 456 401.3 1360 1190 326, 4th 425 325 , 4 - 3800 3650 - 4th - , 7 - , 2 98.2 - 150 103, 4th 100 , 0 103 , 0 95.5 1920 1920 119 5 108 , 0 119 , 3 86.9 2269 2265 110, 70-82 100 7O-82 110 70-82 91.0 2087 , 5 2083 ,8th " 92, 5, 92 4th 92 4th 70 92 , 0 92 0, - 0 6.0 83 83 2, 1 2 - 4th , 0 4th , 0 1, 1 1 1.903 - - 0 , 0569 ι,
10, 1
13th 10 1.323 33 , 747 33 , 747 1.533
12.525 19th , 997 19th , 995 29
118 , 972
, 602 29
116 , 972
, 418

Table II (continued) - 7a -

U.S. Patent 3,897 Example 1

NaOH, parts by weight Na ₂ CO ₃ , H ₂ O,

HCOONa, "^, CH ₃ OH" CD-HCOOCH ₃ , "

β> SO-, " ^ .Na ₂ S ₂ O ₄ , gross amount, _{parts by weight C 0} Na ₂ S ₂ O ₄ , 100% basis J £ purity,%

Temperature range, C Total reaction time, hours Spreading rate, kg / h / l Total Na equivalents

Total formate equivalents """- ---. _{ΛΛ,, Ann} fo

Total SO ₂ equivalents 1.717 1.998 \, izi i, mi, m _ΙΛ _,

Total CH ₃ OH equivalents 14.045 11.704 14.981 14.981 12.172 ^

example 1 , 0 2 , 9 3 • 4th ,8th 5 , 9 28 32 - - 28 - , 17th - 28 - - 150 , 470 125 , 0 120 120 , 0 130 , 0 100 , 717 117 , 0189 78 131 100 450 .045 375 , 52 480 480 , 926 390 , 17th 110 128 , 720 85 85 , 926 110 , 470 steep H2 131 , 998 87 80 , 327 110 , 717 101, 117 , 704 74 ,8th 72 , 981 97 , 172 91 90 86 91 89 72 74 71 - - ·· 7th 8th 7th , 0 8th 7th 0 - - - 2 2 1 , 675 1 2 1 1 1 , 147 1 1 1 1 1 , 327 1 1 14th 11 14th , 981 14th 12th

From the examples of the prior art, the following can be made Conclusions can be drawn:

(a) Sodium hydroxide is routinely used as a supplier for the required alkali has been used;

(b) Sodium carbonate is often mentioned in the relevant prior publications mentioned, but has rarely been used in practice;

(c) in the few exemplary embodiments. which sodium carbonate has been used as a supplier of the required alkali, the yield is in terms of the production of sodium dithionite much less than when using sodium hydroxide.

Nevertheless, it would be extremely desirable for such a process to have sodium carbonate as the main supplier for the required To be able to use alkali, if only because this compound is much cheaper than sodium hydroxide. In addition, the The rate of generation of sodium dithionite per unit of reactor volume is an extraordinarily critical size and economical of particular importance because the reaction in question is relatively slow in itself and therefore takes several approaches Pressure must be reacted in a batchwise process. In DT-PS 2,000,877 and in US-PS 3,877,695 has also already been explained that it is very difficult to measure the performance of such a reaction system to improve decisively, in particular by reducing the amount of alcohol, which together with the sulfur dioxide in the Reactor is fed, in part because

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Water gets into the reaction mixture together with sodium hydroxide, partly as solution water and partly in chemically bound form, while on the other hand the weight ratio of alcohol to water is not significantly lowered can be without significantly increasing the solubility of the dithionite. However, dissolved dithionite decomposes immediately in the pH values prevailing in the reaction, resulting in a reduction in yield and a reduction in the performance of the overall process follows.

It is accordingly an object of the present invention to provide an improved Process for the production of anhydrous alkali metal dithionites and in particular sodium dithionite are available to provide, in which considerable amounts of the sodium ion required by sodium carbonate or by a pre-reaction product made of sodium carbonate and sulfur dioxide. In addition, by means of this improved method, the generation of dithionite per unit volume of the reactor can be increased.

The batchwise process according to the invention for the production of sodium dithionite (Na ₂ SO ₁ J, in which SOp dissolved in methanol is reacted with sodium formate dissolved in water and an alkali at given weight ratios of methanol to water, is characterized in that to increase the amount of formed Na-SO ^ per hour and per unit volume of the reactor while reducing ^ the required amount of sodium component, the following working conditions are observed:

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41 ».

a) Use of dry, powdery sodium carbonate (Na ₂ CO,) as an essential supplier of the required sodium component,

b) use of water only to dissolve the sodium formate,

c) Use of the minimum total amount of methanol required to maintain the specified weight ratio from methanol to water is required and

d) Adjusting the amounts of SO, methanol, sodium formate, water and sodium carbonate for maximum utilization of the reactor volume.

According to the method of the invention, sodium ddthionite is therefore produced using a fixed reactor volume by reacting sulfur dioxide, which is dissolved in methanol, with sodium formate, which is present as a solution in water at a temperature of about 120 ° C., and with sodium carbonate, which is fed into the reactor in the form of a dry powder which already contains a methanol solution. The sulfur dioxide in the form of the methanol solution and the sodium formate in the form of the aqueous solution are also fed into this reactor. Methanol and water are regulated to a predetermined weight ratio and the water is only used in that minimum amount which is necessary to dissolve the sodium formate in maximum concentration at an elevated temperature. The amounts of sulfur dioxide, methanol, sodium formate, water and sodium carbonate are preferably matched to one another in such a way that the specified reactor volume is fully utilized. Each methanol solution contains around 4 % methyl formate. An additional amount of methanol is over

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fed to the reflux condenser in order to keep losses of methyl formate and other by-products as low as possible. This additional amount of methanol is about 15 % of the total methanol. The weight ratio of methanol to water is expediently in the range from about 4.2 to 5.2. The equivalent ratio of sulfur dioxide to methanol is expediently in the range from about 0.20 to 0.25. The weight ratio of sulfur dioxide to water is expediently in the range from about 1.7 to 2.4. The equivalent ratio of sulfur dioxide to pormiation is expediently about 1.4. The amount of sodium carbonate used is expediently about 60 percent by weight of the amount of sodium formate used. The equivalent ratio of sodium carbonate to sodium formate is therefore expediently about 0.8.

The yields of dithionite that can be achieved according to the invention are relatively high and are, based on SO 4, about 74 to 82 %, based on formate about 53 to 59 % and based on sodium about 65 to 75% the reactor volume, the production of dithionite is about 0.2755 kg / l or about 0.0718 kg / h / l.

With regard to the utilization of the Na ₂ O used, the process according to the invention, which essentially uses sodium carbonate, is at least 7 % more effective than the process according to the prior art, which uses sodium hydroxide, as described, for example, in US Pat. No. 3,887 . Although the reasons for this improvement are not

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are completely clear, but it is assumed that when sodium hydroxide is used, the addition of the appropriate proportions of the concentrated sodium hydroxide solution in the reaction medium creates locally strongly alkaline media and thereby _{promotes the formation of by-products such as sodium sulfite (Na 2} SO,), especially sodium sulfite is insoluble and therefore essentially non-reactive. Sodium carbonate, on the other hand, is not immediately dissolved in powder form when it is added and a corresponding alkaline environment therefore develops much more slowly.

However, a comparative calculation of the results obtained according to the state of the art using sodium hydroxide (Na ₃ O) on the basis of the alkaline sodium in relation to the total sodium added may lead to incorrect conclusions lead, for example, if you look at example k of the US-PS

no 3 897 5M used in which / sodium hydroxide is added, but all of the sodium is only supplied in the form of sodium formate. The reason for this is that such a process cannot be continued without recirculating alcohol. To explain this, it should be noted that the desired conversion consumes a total of 1 mole of formic acid and 2 moles of bisulfite, according to the following equation: HCOOH ♦ 2NaHSO> Na ₃ S ₃ O ₁₁ + CO ₃ + 2H ₃ O

If, however, according to example k of US ^{Pat. No. 3,897,5 * »1} » SO _{3 is added} to the sodium formate solution, the result is according to

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the following equation 2 moles of formic acid to 2 moles

Sodium bisulfite: H ₂ O ♦ SO ₂ ♦ 2HCOONa> 2HC00H + 2NaHSO,

The formic acid formed in excess must therefore be mixed with excess methanol to form methyl formate react. If this reaction did not take place, the excess formic acid would be the freshly formed Immediately decompose dithionite. The real problem occurs when the methanol is recovered for a next batch. It now contains the formed ant methyl ester and can lead to serious decomposition of the dithionite in a subsequent test run if such a methyl formate containing methanol was used for the approach of Example 1 of US Pat. No. 3,897,5M. If namely in such a further Test run the excess formic acid is formed, it can no longer be converted to methyl formate, because the corresponding methyl ester is already present in the methanol.

The reaction batches used in the working examples below, in which sodium formate is used either with sodium hydroxide or with sodium carbonate,

containing / based on the assumption that the methyl formate / Methanol comes from a previous test run, so that the added methyl formate is neither consumed nor regenerated. The exemplary embodiments simulate the conditions of a normal production on a commercial scale, in which the

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1"

Methyl alcohol is repeatedly returned to the cycle.

In the original approaches, as they result from the exemplary embodiments of the prior art and in which Sodium hydroxide is used, therefore no methyl formate is fed in either. The formation must therefore be completely supplied by the sodium formate used and the amount of sodium hydroxide must be reduced accordingly.

As a result, those used in the following examples can be used Approaches that correspond to a recycling or recovery of methanol, not literally with the original approaches according to the exemplary embodiments of the prior art Technology can be compared. For this reason, comparisons are also made below on the basis of the total used sodium, although the consumption of less total sodium is less noticeable because of the presence sodium formate dilutes this effect somewhat.

The method according to the invention is therefore essentially described in carried out in the following way:

a) Sodium formate is dissolved in water at an elevated temperature up to its maximum concentration and thereby a obtain aqueous formate solution;

b) sulfur dioxide is dissolved in methanol to form a methanol solution;

c) a methanol solution is placed in a reactor and closed

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the following feeds are added to this / / methanol solution:

1) Sodium carbonate preferably in the form of a dry powder according to a regulated program, whereby a substantial amount of the alkali required for the reaction is made available and the sodium carbonate makes up at least 50 percent by weight of the sodium formate used, based on proportions where the sodium formate 100 % of the required Alkali would provide;

2) an aqueous formate solution corresponding to a second regulated program and

3) the SOp-methanol solution according to a third controlled program, with about 80 % of the solution being added as a rapid feed and the remaining amount of sulfur dioxide being added as a slow feed with an increasingly slow addition rate.

According to a further embodiment of the process according to the invention, even more favorable results are obtained by allowing the sulfur dioxide to prereact with the sodium carbonate suspended in methanol and then feeding the resulting sodium bisulfite slurry in methanol together with the concentrated sodium formate solution at a controlled rate into the _A main reactor. In this embodiment, sodium dithionite is obtained with a favorable particle size and favorable dust properties and a degree of purity which is at least as good as the product obtained according to the standard process using sodium hydroxide,

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as described in U.S. Patent 3,887,695. However, the yield in the process according to the invention is about 22 to 25 % greater than with this standard process, while at the same time about 3.0 Jt less sulfur dioxide and about 8.6 % fewer equivalents of sodium hydroxide are consumed.

According to a further embodiment of the process according to the invention, a slurry of sodium metabisulphite, which has been obtained by stoichiometric conversion of all of the sodium carbonate with about half of the required sulfur dioxide, is produced in a larger amount of methanol and then 60 % of the remaining amount of sulfur dioxide is in the methanol dissolved and the metabisulfite slurry thus obtained is then fed into the main reactor together with the concentrated aqueous solution of the sodium formate. This second embodiment of the process according to the invention also gives sodium dithionite as the end product with excellent properties with regard to particle size and dusting, the yield being improved by 20% compared to the results obtained by the standard process, as described in US Pat. No. 3,897,544 while at the same time about 5.4 % less equivalent sodium hydroxide is consumed.

Contrary to the information in the prior art, thus the use leaves with sodium carbonate · optimal Ver ratio of one reactant and an optimal working implement wise, the sodium carbonate an essential

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Amount of the alkali required for the reaction supplies. That Sodium carbonate can also be used as sodium bicarbonate or, as a result of the preliminary reaction, as sodium sulfite or sodium metabisulfite and to a certain extent also as sodium hydroxide are present. However, sodium carbonate has the particular advantage that it is relatively cheap.

The possibility of replacing sodium hydroxide with sodium carbonate in the standard procedure as described in U.S. Patent 3,887,695 has been investigated by substituting corresponding equivalent amounts of sodium carbonate instead of Sodium hydroxide was used, but the same amount of water was used, with that being chemically bound in the sodium hydroxide Water was included in the calculation. In this way, however, undesirable dusty products were obtained and the end product was revealed a low degree of purity. The amount of sodium carbonate was then reduced somewhat, but all other process variables were kept constant. This is how purity became of the end product and reduces the amount of dust.

In a number of examples, the addition of 45 g less total amount of sodium carbonate the dust number of 350 decreased to 307. Another reduction in dust levels 215 was possible by delaying the addition of sodium carbonate by 5 minutes. The best results on a However, a reduction in the number of dusts was achieved by dividing the total amount of sulfur dioxide, as can be seen from the The result of the following comparative examples shows:

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Distribution ratio of dust number from S0 "

81/19 260

82/18 196

83/17 1 * 7

8M / I6 97

The dust properties of the final sodium dithionite products obtained in such a batch process is measured by means of a colorimetric analysis method in which a fuchsine solution is used to determine the powdery sodium dithionite in a sample. In this analytical method, 25 ml of a fuchsine solution with 0.0256 g of sodium dithionite are used to determine the dust number of each production sample implemented and discolored.

A special device is used to carry out this evaluation method. It consists of a carefully cleaned and dried mud pipe 2.5 * 1 cm inside diameter and 86.36 cm in length, with a ball lock at each end, which is clamped in a vertical position. An equally carefully cleaned and dried mud pipe for the too The test sample with an inside diameter of 2.5 * 4 cm and a length of 20.32 cm, which at the lower end has a glass wool pack of about 2.5 * 1 cm in length, is placed in an upright position Position connected to the bottom of the slurry tube. The floor of the tube containing the sample is with a nitrogen source, which is under a pressure of 0.35 to 0.70 kg / cm

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is in communication via a needle control valve and a rotameter. In addition, a J-shaped discharge pipe (inner diameter H to 5 mm) is connected in an inverted arrangement at the upper ball lock end of the slurry tube, with the straight leg of the "J" extending into one up to a distance of 2.5 ¹ J cm from the floor graduated cylinder of 500 ml capacity, containing ^ 50 ml of water. A door blade buzzer is connected to the bent end of the J-shaped discharge pipe and is connected to a power source via a control device (Variäc). At the top of the graduated cylinder there is a 50 ml burette containing the fuchsine solution.

At the beginning of the examination, a bottle containing a sample of the product to be examined is gently rolled and rotated, in order to mix the contents carefully in this way. If, on the other hand, the contents of the bottle are shaken too vigorously, Clouds of dust settle on the bottle head, which then prevent reproducible results during the examination.

W.

A 50 g sample (error limit - 0.1 g) is then taken from the bottle and carefully transferred into the receiving tube for the slurry test, being careful not to lose any dust particles during the transfer _; and a camel hair brush is used to transfer residual particles into the sample tube.

Then add 3.0 ml of the fuchsine solution to the water in the graduated cylinder. Then you set the vibration

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device in gear and controls it in such a way that the vibration tappet of the doorbell buzzer sharp against the underside of the J-shaped drainage pipe roughly in the center of the bent part erupts. If the buzzer, properly set and through the Control unit is controlled, the examining laboratory technician can feel the vibrations directly when he pingers on the pipe applies at a distance of about 7.62 to 10.16 cm from the point where the vibration plunger strikes. If however, if the entire arrangement is clamped too tightly, the vibrations are dampened and are then no longer effective to set the dust settling inside and outside the discharge pipe in motion again.

Then carefully open the needle valve that controls the flow of nitrogen gas through the slurry column, with a flow rate of 2668.9 cm ^ / minute adjusts. This flow rate is maintained during the entire test run. As soon as the nitrogen stream enters the bottom of the slurry tube and Passing through the sodium dithionite sample is sufficiently strong to form a cloud of dust, becomes a timing device set.

At the point in time when the fuchsine solution is decolorized, a further few milliliters of the fuchsine solution are added. The number of milliliters increases at one-minute intervals Fuchsine solution recorded. The slurry tube is left run for about 5 minutes (deviation - 0.5 minutes). The overall

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volume of fuchsine solution is determined to be about 0.1 ml and the lapse of time is determined to 0.1 minute.

The dust number is calculated according to the following equation:

Milliliters of _{fuchsine solution χ 3Q s dust count} time in minutes

In general, the amount of SO _{2 added is separated} into two partial amounts. The quickly added amount of SO is about 80 to 85 % of the total amount and is added over the course of the first 80 minutes. The slowly added ^so ₂ ~ amount, ie the remaining amount, is added within the next 80 minutes. The reaction mixture is then allowed to react further for the next 80 minutes without any further addition, only the rinsing alcohol flowing in, which is used to prevent a loss of volatile reactants.

the amounts of In further experiments will / additional water and to additional methanol, which are required when using sodium hydroxide, is reduced and finally the proportions of the individual reactants are coordinated so that the total volume of the reactor is used in order to achieve a maximum production of dithicnite per unit volume of the available reactor volume. In the following examples 2, 3, * ♦, 6 and 7 the results of experiments with sodium carbonate on a laboratory scale and in technical work are explained and the

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Results are compared with those obtained according to Examples 1 and 5 can be achieved using sodium hydroxide, as well as the results of the prior art (15 examples) using sodium hydroxide and sodium carbonate together.

The individual conditions and results for Examples 1 to 4 are summarized in Table III below. Example 1 corresponds to the average values of 7 test runs using sodium hydroxide with a degree of purity of 99% in the form of a 73 percent solution without the use of sodium carbonate according to a method as described in US Pat. No. 3,887,695, which was carried out on a laboratory scale . Example 2 shows the results using equivalent amounts of sodium

the carbonate and / same amounts of water as in example 1.

Example 3 shows the results using a smaller amount of sodium carbonate and the same amount of water as in Example 2. In Example 4 are even smaller amounts of sodium carbonate, but also smaller amounts of water and Methanol.

A typical procedure, as used inter alia for Example 2, is detailed below explained:

A stirred reactor is charged with a mixture of 851 g of methanol and 38 g of methyl formate. These

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Charge is heated to 70 ° C and under a nitrogen blanket

2 pressure of 2, M5 kg / cm held.

In addition, a mixture of 828 g of sodium formate (degree of purity 96X) and 727 g of water is practically boiling heated. This mixture is then transferred to a stainless steel cylinder which is surrounded by a steam jacket (Steam with a pressure of M, 9 kg / cm) to do this to keep the solution at a temperature above 1Ί8.9 ° Ο. The liquid level in this storage vessel is determined by means of a float to which a metal rod is attached. which protrudes from the cylinder head into a sight glass. This sight glass is calibrated in millimeters, so that the liquid volume in the storage vessel with a high degree of accuracy is known. The feed rate is controlled by reading the liquid level per millimeter and comparing it with a calculated value.

In addition, another is in the same way with sight glass and indicator rod equipped stainless steel cylinder charged with a mixture of 1702 g of methanol, 76 g of methyl formate and 1307 g of sulfur dioxide. Even with this one second reservoir can be the volume of liquid with determine good accuracy. The feed rate of the mixture is regulated by means of a rotameter.

100 g of sodium carbonate and a

sixth beaker weighed out 75 g of sodium carbonate. The GE-

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The total amount of sodium carbonate is therefore 557 g · The feed device for this sodium carbonate consists of a filling funnel with two valves. This filling funnel holds a good 100 g of material. The space between the two valves contains approximately 11.1 grams of material. Since a total of 557 g of sodium carbonate have to be fed in over the course of 79 minutes, 7.05 g of sodium carbonate should be fed in per minute are fed. Since 11.1 g of sodium carbonate can be fed out per batch, the valve system should be running every 1.57 minutes be set. A side stream of nitrogen is fed in at the inlet opening for the sodium carbonate in order to prevent condensation products from occurring during the reaction this inlet becomes clogged. In later experiments this nitrogen sidestream is omitted and valves are used instead and connecting pieces heated by means of an electrically heatable belt so as to prevent condensation.

Once the reactor contents are adopted a temperature of 70 ⁰ C, the SO methanol solution is fed. After the reaction mixture has reached a calculated SO concentration of 1 % , a timer is started and the sodium formate solution and the solid sodium carbonate are then fed in. 5 t of the sodium formate solution are fed in within the first minute and the remaining 95 t are fed in during the remaining 79 minutes. The sodium carbonate is fed in over 79 minutes at a rate which corresponds to the rapid SO feed. 81 % of the SOp methanol solution is fed in within the first 80 minutes and the remaining 19 % is fed in at an increasingly slower rate in the subsequent 80 minutes.

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At the end of this second 80 minute period, the SOp-methanol solution feed rate is decreased to about one third of the fast feed rate and this rate is maintained for the next 20 minutes. The feed speed is then reduced to 26% of the fast feed speed and held at this value for about 15 minutes. Finally, the rapid feed rate is reduced to 17 % until all of the SOp / methanol solution has been fed in. This generally takes about 160 minutes.

The reaction temperature is at the start of reaction 70 ° C and allowed to within from about 5 minutes to 83 ⁰ C increase. This temperature value of 83 ^° C. is then maintained until the end of the test run.

After the period of slow addition of the SO-methanol solution has ended (i.e. about 160 minutes after the start of the reaction) the reaction mixture is left to stand for a further 80 minutes,

until a total of 20 minutes has passed since the start of the experiment are.

During the entire test run, 500 g of methanol are fed to a washing device in order to reduce the loss of volatile reactants such as methyl formate and SO ₃ .

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At the end of the first 80 minutes, i.e. after the rapid supply of SO- and after 160 minutes, i.e. after Termination of the slow addition of SO., And after termination During the test run, i.e. after 240 minutes, samples of the piltrate of the reaction mixture are tested. A 10 ml sample is made mixed with an alkaline formaldehyde solution in order to bind the bisulfite present in it and then with a 0.1 N standard iodine solution titrated. The titer value determined is a measure of the sodium thiosulphate content of the solution and thus a measure of the degree of decomposition of the dithionite formed.

The reactor contents are filtered through a Buchner funnel fitted with a glass frit, leaving a protective atmosphere Nitrogen is maintained to prevent any contact of the reaction product with air. The conversion product is then washed with methanol and dried in a vacuum bottle by heating in a hot water bath under vacuum. The dried product is weighed and the yield as well as the degree of purity and the number of dusts are determined. Besides that a sieve analysis is carried out.

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ORIGINAL INSPECTED

Table III

Production of sodium dithionite on a laboratory scale

example

NaOH, g * 121 , 9 _- ,8th - , 6 - H ₂ O, g 155 - - - Na ₂ CO ₃ , g - 557 517 501 HCOONa (96Ϊ), g 787 , 775 828 , 311 828 , 931 819 H ₂ O, g 155 727 727 595 CH ₃ OH, g 1702 , 073 1702 , 073 1702 , 073 1206 HCOOCH ₃ , g 76 , 012 76 , 101 76 , 012 76 so ₂ , g ' 1282 , 625 1307 , 210 1282 , 625 1263 CH ₃ OH (submitted), g 851 851 851 851 HCOOCH ₃ (submitted), g 38 38 38 38 HCOONa (submitted), g Il - - - H ₂ O (submitted), g 22nd - - - CH ₃ OH (scrubber), g i »50 500 150 I50 Na ₂ S ₂ O ₁₁ , g 1129 1162 1116 II32 Degree of purity, % 90 89 91 90.9 pure Na ₃ S ₂ Oj ₁ , g 1299 1313 1297 13OI Dust count 175 153 97 238 Total ^ Na equivalents 22nd 22nd 21 21.196 Total formate Equivalents 11 11 11 13.91 Total SOg equivalents 20th 20th 20th 19.716 Total CH, OH equivalents 95 97 95 80.111

χ 99 % purity

73 percent solution

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Examples 5 to 7

These examples show the results of trials carried out on a pilot scale, one trial using sodium hydroxide and two trials using sodium carbonate. The results obtained are summarized in Table IV. The reactor described in US Pat. No. 3,887,695 is used to carry out the experiments, and the experiments are carried out in the manner described therein. The amount of sodium carbonate used is 63 percent by weight of the sodium formate used. In Example 6, the amount of methanol is the same as in Example 5, but the amount of water is slightly higher than in Example 5. In Example 7, the amount of water has been reduced by 25% compared to Example 6 and the amount of methanol has been reduced by 20%.

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example

Table IV

Semi-technical tests 5 6

NaOH, parts by weight

Na ₂ CO ₃ , " H ₂ O,

HCOONa, " CH ₃ OH, ■ " HCOOCH ₃ , " so ₂ ,

Na-S-O-, gross amount, Gemdts-

^Λ * ⁴ parts

Na ₃ S ₃ O ₄ , 100% basis Degree of purity,% dust count Total reaction time, hourly yield, kg / 1 total Na equivalents total formate equivalents total SO ₂ equivalents total CI ^ OH equivalents 71

83 83 98 116 87 138 138 138 501 501 4OO 18th 18th 18th 211.2 205.2 205.2 246 239 247.5 226 222 228.7 92 92.7 92.4 100 206 102 4.0 4.0 4.0 0.2707 0.2707 0.3234 3.704 3.514 3.514 2.247 2.247 2.247 3,300 3.206 3.206 15.937 15.937 12.784

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Tables Va and Vb show calculated ratios of the reactants used from the experiments which have been described in Tables I to IV. In addition, yield values are given, based on SOp or on pormiation or on sodium. These calculations were carried out both for the exemplary embodiments and for the examples according to the prior art. Finally, the calculated values for the yield are also given based on the unit volume of the reactor per hour. In general it can be stated that in the tests carried out on the laboratory scale the yield was increased by 18 % and in the tests carried out on the semi-industrial scale by 20 Jt.

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Table Va

example

Experimental results 3 4 5

Equivalent ratio NatSO ₂ equivalent ratio NaiFormiat 'weight ratio CH ₃ OHtH ₂ O equivalent ratio of SO _2: CH ₃ OH weight ratio of SO _2: H ₂ O equivalent ratio of SO _2: formate * Yield: SO-'Basis,%

Formate base,% sodium base,% yield, kg / h / l

1.138 1.133 1.096 1.090

1.618 1.612 1.558 1.542

4.842 4.283 4.209 4.310

0.209 0.206 0.209 0.246

2.027 1.797 1.762 2.121

1.422 1.422 1.422 1.414

74.6 74.0 74.4 75.8

53.0 53.6 52.9 53.6

65.5 67.5 67.9 69.5

0.0587 0.0587 0.0587 0.0682

1.119 1.093 1.093

1.648 1.564 1.564

5.204 4.396 4.702

0.207 0.202 0.252

2.161 1.774 2.366

1.473 1.431 1.431

78.7 79.5 81.9

57.8 56.7 58.5 70.1 72.6 74.8

0.0587 0.0587 0.0682

including the formate equivalents in Na formate and methyl formate

xx

including the methanol equivalents in the methyl formate

US patent

Table Vb

State-of-the-art results
3 887 695 3 411 875. 3 714 340

- 32 -

3 897 544

Equivalent ratio Na: SO ₂ 4, 1.126 1.187-1.402 1,211-1,343 1.261-1.451 Equivalent ratio Na: formate ^x 0, 1.688 1.397-1.680 1.365-1.657 1,000-1,476 _{CH 3} OHtH ₃ O weight ratio 233-4,313 2.081-4.235 2.995-4.331 2.996-3.995 Equivalent ratio SO ₂ : CH ₃ OH ** 0, 253-0.257 0.085-0.118 0.118-0.158 0.089-0.171 «Α Weight ratio S0_: H_0 2.180 0.399-0.999 0.734-1.033 0.708-1.023 O
CO
0 »
0 » Equivalent ratio S0_: formate
Yield: S0_ basis,% 70 253-0.257
80.0 1,026-1,415
65.5-70.0 0.118-0.158
65.1-78.6 0.089-0.171
63.0-68.3 ^ ^ v Formate base,% 60.0 34.0-49.0 37.7-50.4 21.7-39.9 CO
cn Sodium base,% , 9-71.1 48.1-58.4 52.4-60.8 43.4-54.0 Spreading rate, kg / h / l 0.0569 0.0228 0.0257-0.0351 0.0189

including the formate equivalents in Na formate and ethyl formate

XX

including the methanol equivalents in the methyl formate

From the table values it can be seen that with regard to the equivalent ratio of sodium to SO “there is a small difference between Examples 1 and 5, which work with sodium hydroxide, the three Examples H , 6 and 7, which work with sodium carbonate and the examples of mainly for the State of the art to be used consists of four US patents. The use of sodium carbonate enables a 3Ϊ lower equivalent ratio of total sodium to SO ₂ compared to the best results of the prior art. Although a higher weight ratio of methanol to water was used in the laboratory-scale or pilot-scale examples using either sodium hydroxide or sodium carbonate than in the fifteen prior art examples, the corresponding ratios for sodium carbonate are in the five concerned Examples slightly lower than the corresponding proportions for sodium hydroxide in the remaining two examples, namely

/ In terms of both laboratory and semi-industrial scale. / the weight ratio of sulfur dioxide to water shows that the examples on the laboratory or semi-industrial scale have higher values than three out of four publications according to the prior art. The equivalent ratios of sulfur dioxide to pormate in the laboratory tests and the semi-technical tests are markedly higher than in the prior art, both when sodium hydroxide and sodium carbonate are used.

The particular advantages of the process according to the invention are

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but clearly when you look at the yield figures and the calculated ones Taking product yield into account. In the examples carried out on a laboratory scale, the replacement of sodium hydroxide leads by sodium carbonate in Example 4 compared to Example 1 to an increased performance with respect to the desired Product, considering all three starting materials. This increase in performance is measured as that Number of dithionite product produced per hour and per liter of reactor solution and this amount of product produced is through the Replacement of sodium hydroxide with sodium carbonate also improved. Corresponding improvements in terms of effectiveness the method and the productivity are compared with the pilot plant run of Example 7 with Example 5 observed.

The results are particularly convincing with regard to the high purity values and the low dust levels of the products of Examples 6 and 7, which emerge from Table IV, as having such properties for industrial use as bleaching agents are highly desirable.

Additional pilot results are summarized in Table VI for a trial run using of sodium hydroxide and two experimental runs using sodium carbonate, the proportion of sodium carbonate 62.9 percent by weight of the amount of sodium formate used.

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Table VI

example

Attempts in the 8th

semi-industrial scale 9 10

Na ₂ CO ₃ , kg fed - 45.36 45.36 NaOH, kg added ³ * 31.75 - - VV
HCOONa, kg added 60.10 72.12 72.12 SO ₂ kg fed in 95.71 110.22 110.22 CH ₃ OH, kg fed 227.25 219.09 219.09 (presented amount) (64.41) (74.39) (74.39) (together with S0 ~) ( 128.82) (110.68 j (11O, 68) (Washer) (.34.02) (.34.02) (34.02) H-O, kg added 45.36 47.17 47.17 (together with NaOH) ill, 79y - - (together with HCOONa) (33.57) (47.17) (47.17) HCOOCH ₃ , kg 8.16 7.71 7.71 Total volume, 1 378.53 378.53 378.53 Filtrate volume, 1 329.32 317.97 317.97 Product, kg 112.04 136.98 134.26 Product,% Na ₂ S ₂ O ₄ 91.5 90.3 90.3 pure Na ₂ S ₂ O ₄ , kg 102.51 123.83 121.11 Yield, kg / 1 0.2707 0.327 0.3198 Yield: S0 ₂ ~ basis,% 78.7 82.5 80.8 Formate basis,% 66.6 67.0 65.7 Sodium base,% 70.2 74.2 72.7 Spreading rate, kg / h / l 0.0682 0.0814
■ ■ * 0.0814

100% pure

xx

100% pure

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In Examples 9 and 10, significant improvements in terms of yield increase have been achieved, as can be seen from result in the specified values for the production of pure sodium dithionite per liter of reactor volume. Although the amount of water which was used to dissolve the increased amount of sodium formate is only slightly higher than that in Example 8 Total amount of water used, in which sodium hydroxide was used in combination with sodium formate, enables it the replacement of sodium hydroxide with sodium carbonate to decrease the amount of methanol, although additional sulfur dioxide was applied. Since methanol has a comparatively lower density than water, this leads to a reduction in the amount of methanol to the fact that a considerable amount of valuable reactor space is saved.

In general, it enables sodium carbonate to be used as the main supplier of the alkali in the process according to the invention (See. Examples 8 to 10 ^ less solvents and larger

Amounts of reactants in a reactor of a given capacity

like to use so that / the performance of a reactor in comparison with known standard processes using sodium hydroxide as the main supplier of alkali, quite considerably

leaves. /
improve / In addition, less sodium is required overall,

if sodium carbonate is used as a reaction component.

The following further examples illustrate the use of sodium carbonate in solid form, but can be used within the scope of the invention also add some water together with the sodium carbonate

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can be used if at the same time the water content in the other feed streams is correspondingly reduced. In which According to the method according to the invention, it is therefore essential that the total amount of water that is fed to the reactor is as small as possible is, and that a predetermined MethanolιWasser ratio is maintained, but the amount of water is uneven can be distributed to the individual feed streams.

Example 11

This example illustrates an embodiment in which sodium carbonate is allowed to pre-react with sulfur dioxide in order to achieve this Manufacture feed material.

Three different feeds are made. Feed "A" is obtained by suspending 83 parts by weight of sodium carbonate in 167 parts by weight of methyl alcohol containing 9 parts by weight of methyl formate and then adding 167 parts by weight of sulfur dioxide. Feed "B" is obtained by dissolving 13 parts by weight of sodium formate with a degree of purity of about 96 tons in 93 parts by weight of water. Feed ¹¹ C ″ is obtained by dissolving 35 parts by weight of sulfur dioxide in 35 parts by weight of methyl alcohol which also contains 2 parts by weight of methyl formate.

A charge of 115 parts by weight of methanol containing $ parts by weight of methyl formate is placed in a reactor. This feed is stirred and heated under a pressure of 1, ¹ J kg / cm to a temperature of 65 ⁰ C. The infeeds "A" and ¹¹ B "then become simultaneously

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fed in at the rate that each feed would be fed in individually within the first 80 minute period. The reactor contents are heated until a temperature of 83 ° C. is reached, whereupon the heating is reduced and the temperature is kept at 83 ^° C. For heating of the reactor contents from 65 ⁰ C to 83 ° C etwa.10 minutes are required. After this heating-up period, the reactor pressure has risen to an overpressure of 3 »50 kg / cm as a result of the formation of CO_ in the course of the reaction. The overpressure in the reactor is then kept at this value by letting the carbon dioxide formed out of the reactor in a controlled manner. This discharged gas passes first through a water-cooled condenser (35 ° C) and then a cooled condenser (-1O ⁰ C) and finally, which is charged with methanol at a rate of 0.26 parts by weight per minute through a cooled scrubbing. The condensates from the two condensers and the effluent from the methanol scrubber are returned to the reactor together.

At the end of the first 80 minute period, feed "C" is also fed at a rate of 1.5 parts by weight per minute. After 15 minutes the feed rate is reduced to 1.0 parts by weight per minute and after an additional 15 minutes the feed rate is reduced to 0.7 parts by weight per minute. Purely the addition of a total of 72 parts by weight feed "C" therefore takes 80 minutes. The temperature in the reactor also rises while this feed (C) is being fed in

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Maintained 83 ° C and the overpressure to 3.50 kg / cm.

The same conditions are maintained for an additional 70 minute period after the feed of feed (C) is completed. After the lapse of 230 minutes reckoned from the start of the reaction, the reactor contents is cooled to 6O ⁰ C and filtered. The filter cake is then washed with 2M0 parts by weight of methanol and dried in vacuo. In this way, 2 ^ 0.5 parts by weight of a crystalline product is obtained which consists of the desired sodium dithionite with a degree of purity of 92.3 % .

Example 12

This example illustrates the use of sodium metabisulfite as a feed material.

In this case, too, three different feeds are made. Feeding in "A" is obtained _/ by suspending 15Ο parts by weight of sodium metabisulfite in I67 parts by weight of methyl alcohol, which contains 9 parts by weight methyl formate, and then adding 67 parts by weight of sulfur dioxide to the suspension. Feeds "B" and "C" correspond to those of Example 11.

The reaction is carried out in the same manner and with the same total reaction time as described in Example 11 is. After filtering the contents of the reactor, washing and drying as described in Example 11, 238 weight percentages are obtained

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int

parts of a crystalline product, which consists of sodium dithionite with a degree of purity of 91 % .

As already mentioned above, this according to the invention enables Process. To increase the efficiency of the reaction per unit volume of a given reactor per hour significantly.

/ Ante il

This performance improvement is based on the fact that a larger / of the total reactor volume can be used for the production of sodium dithionite than was previously possible.

According to the invention, less water is used and therefore Less methanol can also be used while maintaining the required ratio of water to methanol in the reactor can be. As a result of the use of less methanol, more space is then available in the reactor, so that a larger amount of end product can be generated per reaction batch. Although other alkali compounds are also within the scope of the invention can be used, sodium carbonate is preferred.

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Claims (1)

Claims (V, Paragraph-wise process for the production of sodium dithionite (Na _{2 SpO 1.} ), In which SO ₃ dissolved in methanol is reacted with sodium formate dissolved in water and an alkali at given weight ratios of methanol to water, characterized in that to increase the amount of Na ₂ SO formed per hour and per unit volume of the reactor with a simultaneous reduction in the required amount of sodium component, the following working conditions are observed: a) Use of dry powdery! Sodium carbonate (Na ₂ CO) as an essential supplier of the necessary sodium component; b) use of water only to dissolve the sodium formate; c) using the minimum total amount of methanol required to maintain the specified weight ratio of methanol to water and d) Adjusting the amounts of SO ₃ , methanol, sodium formate, water and sodium carbonate to maximize the use of the reactor volume. 2. The method according to claim 1, characterized in that a first subset of the minimum for the production of the SO ^ solution required total amount of methanol is used. 3. The method according to claim 2, characterized in that the partial amount of methanol makes up about 50% of the total amount of methanol. 709881/0954 9RIGINAL INSPECTED Ί. Method according to claim 3> characterized in that the weight ratio of SO. to the first portion of methanol is about 1: 1. 5. The method according to claim 4, characterized in that the for the production of the SO_-solution one used methanol Contains first portion of methyl formate. 6. The method according to claim 5 »characterized in that a second portion of the minimum required total amount of methanol, a second portion of methyl formate contains, is presented in the reactor and that in this mixture the aqueous sodium formate solution, the methanolic SO_ solution and dry powdered sodium carbonate are fed. 7. The method according to claim 6, characterized in that the partial amount of methanol presented in the reactor is about 3 ¹ J % of the minimum required total amount of methanol. 8. Embodiment according to claim 1, characterized in that the sodium carbonate component is pre-reacted _{with a proportion of the required SO 2 outside the main reactor.} 9. The method according to claim 8, characterized in that the sodium carbonate component and the partial amount of S0_ with formation a bisulfite slurry is prereacted in a portion of the total required methanol and that this methanolic Slurry together with the aqueous sodium formate solution in 709881/0954 the main reactor is fed. 10. The method according to claim 9 »characterized» that the remaining SOp portion in the remaining portion of methanol is dissolved and this methanol solution is fed into the main reactor. 11. The method according to claim 10, characterized in that the remaining SO partial amount makes up about 20% of the total SO _2. 709881/0954